Patent Documents 1 and 2 disclose the above type of medical instrument. Patent Documents 1 and 2 disclose a medical instrument that includes elastic members that are formed in the shape of a leaf spring, and provided at one end of the medical instrument, and opening-closing members that are provided at the other end of the medical instrument, wherein the opening-closing members intersect each other at a pivot so that the opening-closing members can be opened and closed, and a functional part that implements an incision operation, an excision operation, a gripping operation, a holding operation, a cutting operation, or the like (hereinafter referred to as “incision, excision, or the like”) is provided at the end of each of the opening-closing members. The medical instrument having such a configuration makes it possible to finely adjust the motion of the functional parts by changing the pressing force applied to the elastic members, and is advantageous for surgery and the like for which a fine motion is required.
A very thin membrane, a microscopic blood vessel, a nerve, or the like may be incised or excised using scissors during heart or brain surgery, for example. In this case, body tissue situated in the vicinity of the membrane or the like may be damaged when the edge of the blade moves unintentionally even in a small amount. However, known scissors have a tendency in which the edge of the blade springs immediately after completion of incision or excision. Therefore, the user must finely adjust the force applied to the manipulation members so that the edge of the blade does not spring immediately after completion of incision or excision. This imposes a heavy burden on the user. This particularly applies to brain or heart surgery in which a very thin membrane, a microscopic blood vessel, a nerve, or the like is repeatedly incised or excised.
Patent Document 1 discloses a technique that makes it possible to adjust the spring properties of the elastic member of the medical instrument (e.g., scissors). Paragraph 0007 of Patent Document 1 states that “Operability and usage (e.g., required pressing force or hardness) when the user applies force differ depending on the repulsion force and the flexing properties of the spring 104. The repulsion force and the flexing properties of the spring 104 differ depending on the shape and the material of the spring 104, and affect operability and usage (e.g., hardness increases when titanium is used)”. The surgical instrument disclosed in Patent Document 1 is configured so that the repulsion force and the flexing properties of the spring are changed by forming a plurality of grooves in the plate-like member (spring) so that the operability of the functional part can be adjusted.
However, the surgical instrument disclosed in Patent Document 1 cannot solve the problem in which the edge of the blade springs immediately after completion of incision or excision.
It is effective to use an elastic member having low spring properties (i.e., having a small modulus of elasticity) in order to prevent a situation in which the edge of the blade springs. Since the user who incises or excises a very thin membrane, a microscopic blood vessel, a nerve, or the like attaches much importance to the sensation through the edge of the blade, it is preferable that the spring properties of the elastic member be as low as possible. However, when the spring properties of the elastic member are decreased, the edge of the blade may easily move due to the weight of the manipulation member or the opening-closing member, or may not promptly return to the original position after completion of incision or excision. Therefore, the spring properties can be decreased only within a limited range.